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United States Patent |
6,265,836
|
Aoki
|
July 24, 2001
|
Image distortion compensating apparatus
Abstract
The invention provides a center pincushion distortion compensating reactor
with a simplified construction including two horizontal compensation
coils, one vertical compensating coil, and a magnet for generating a bias
magnetic field. A horizontal deflection current is passed through the two
horizontal compensation coils, and the vertical compensation coil is
modulated with the period of a vertical deflection current such that a
magnetic field is generated in a direction opposite to the bias magnetic
field thereby changing the impedance of the horizontal compensation coils
so as to compensate for a center pincushion distortion on the left and
right sides of a screen.
Inventors:
|
Aoki; Kyousuke (Fukushima, JP)
|
Assignee:
|
Sony Corporation (Tokyo, JP)
|
Appl. No.:
|
265859 |
Filed:
|
March 11, 1999 |
Foreign Application Priority Data
| Mar 13, 1998[JP] | 10-063276 |
Current U.S. Class: |
315/370; 315/364 |
Intern'l Class: |
G09G 001/04 |
Field of Search: |
315/368.26,368.28,370,371,383,364
|
References Cited
U.S. Patent Documents
4827193 | May., 1989 | Watanuki et al. | 315/371.
|
4916365 | Apr., 1990 | Arai | 315/383.
|
5804928 | Sep., 1998 | Endo | 315/371.
|
Foreign Patent Documents |
5-3189 | Jan., 1993 | JP.
| |
9-149283 | Jun., 1997 | JP.
| |
Primary Examiner: Wong; Don
Assistant Examiner: Nguyen; Hoang
Attorney, Agent or Firm: Kananen; Ronald P.
Rader, Fishman & Grauer
Claims
What is claimed:
1. An image distortion compensating apparatus including a center pincushion
distortion compensating reactor, said center pincushion distortion
compensating reactor including:
two horizontal compensation coils connected to each other in series;
one vertical compensation coil; and
a pair of magnets for applying a bias magnetic field to said horizontal
compensation coils and said vertical compensation coil,
wherein a horizontal deflection current is passed through said two
horizontal compensation coils,
and wherein said vertical compensation coil is modulated with the period of
a vertical deflection current such that a magnetic field is generated in a
direction opposite to said bias magnetic field thereby changing the
impedance of said horizontal compensation coils so as to compensate for a
center pincushion distortion on the left and right side of a screen.
2. An image distortion compensating apparatus according to claim 1, wherein
said two horizontal compensation coils are wound in directions such that
the directions of magnetic fields generated by said two horizontal
compensation coils become opposite to each other.
3. An image distortion compensating apparatus according to claim 1, wherein
said vertical compensation coil is wound in a direction such that the
direction of a magnetic field generated by said vertical compensation coil
is opposite to the direction of said bias magnetic field.
4. An image distortion compensating apparatus according to claim 1, wherein
the current applied to said two horizontal compensation coils is a current
with a sawtooth waveform and the current applied to said vertical
compensation coil is a current obtained by rectifying a current with a
sawtooth waveform.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image distortion compensating apparatus
for compensating for an image distortion of a CRT (cathode ray tube) used
in a television receiver or a display monitor, and more particularly to an
image distortion compensating apparatus with a simple construction for
compensating for a center pincushion distortion on left and right sides of
a screen.
2. Description of the Related Art
When an image is formed on the front screen of a CRT of a television
receiver by means of deflection of an electron beam, the image includes a
pincushion distortion.
The pincushion distortion refers to a horizontal line distortion in a
vertical direction or a vertical line distortion. Various methods and
apparatuses for compensating for such distortions have been proposed.
However, even after compensating for such distortions, there can still be a
residual center pincushion distortion (i.e., an "inner vertical-line
pincushion distortion") on the front screen.
FIG. 1 is a front view of a front screen, which schematically illustrates a
center pincushion distortion and the principle of compensating for such a
distortion. In FIG. 1, O denotes the vertical center line of the screen.
In the CRT, if distortion is compensated for such that good linearity is
obtained at the left and right ends of the screen, there can be a large
residual nonlinear distortion near the center line O as represented by
solid lines in FIG. 1.
A pincushion distortion compensating circuit for compensating for such a
center pincushion distortion has been proposed (disclosed for example in
Japanese Examined Patent Publication No. 5-3189).
This distortion compensating circuit is constructed as follows. That is, in
a horizontal deflection circuit, which includes a horizontal deflection
coil and a sigmoid distortion compensation capacitor and which is driven
by a power supply modulated by a vertical synchronization parabolic-wave,
a secondary winding of a voltage-current conversion transformer is
connected between the horizontal deflection coil and the sigmoid
distortion compensation capacitor and a voltage having a maximum value at
the center of the vertical synchronization period is applied to the
primary winding of the above-described transformer.
In recent years, as the front screen of CRTs becomes increasingly flat, the
deflection angle tends to become greater.
Because upper and lower areas of the screen of the CRT are more distant
from the deflection center than a central area of the screen, the upper
and lower areas need a lesser amount of compensation for the sigmoid
distortion than the central area.
Therefore, if the sigmoid distortion is compensated for using a
conventional sigmoid distortion compensating circuit, the sigmoid
distortion is overcompensated in the upper and lower areas compared to the
central area.
This makes it difficult to completely compensate for the pincushion
distortion represented by the solid lines in FIG. 1 and it becomes
necessary to compensate for the sigmoid distortion to a greater degree.
The difference in distance with respect to the deflection center between
the upper/lower areas and the central area of the screen becomes greater
and thus a greater distortion occurs.
To solve the above problem, an apparatus for compensating for the inner
vertical-line pincushion distortion has been proposed (disclosed for
example in Japanese Unexamined Patent Publication No. 9-149283).
In this image distortion compensating apparatus, the amount of sigmoid
distortion compensation in the horizontal deflection is varied depending
on the amount of vertical deflection by controlling the inductance of a
saturable reactor, through which the horizontal deflection current is
passed, depending on the vertical deflection current.
This image distortion compensating apparatus uses a saturable reactor
including four reactor coils connected to each other in a series fashion
and also connected in series to the horizontal deflection coil so that the
horizontal deflection coil is passed through the four reactor coils, a
magnet (i.e., a permanent magnet) around which the four reactor coils are
wound such that magnetic biases are applied in opposite directions to two
respective ends of the set of four reactor coils, and another coil which
is connected in series to the vertical deflection coil so that the
vertical deflection current is passed through this coil thereby
controlling the inductance of the four reactor coils.
In. CRTs, as described above, it is required to prevent image quality
degradation caused by center pincushion distortion (inner vertical-line
pincushion distortion) which can occur on the left and right sides of the
screen, and various techniques of compensating for such a distortion are
proposed.
However, in the distortion compensating apparatus disclosed in Japanese
Unexamined Patent Publication No. 9-149283, the saturable reactor needs
four reactor coils (i.e., horizontal compensation coils).
Furthermore, the magnet for producing bias magnetic fields in opposite
directions can cause a leakage magnetic field, and thus landing has to be
taken into account.
Thus, it is an object of the present invention to provide a small-sized
image distortion compensating apparatus with a simplified construction
including a lesser number of horizontal compensation coils and requiring
no particular consideration on the landing effects, capable of being
produced at less cost.
SUMMARY OF THE INVENTION
According to an aspect of the invention, to achieve the above object, there
is provided an image distortion compensating apparatus including a center
pincushion distortion compensating reactor, wherein the center pincushion
distortion compensating reactor includes:
two horizontal compensation coils connected to each other in series; one
vertical compensation coil; and
a pair of magnets for applying a bias magnetic field to the horizontal
compensation coils and the vertical compensation coil.
A horizontal deflection current is passed through the two horizontal
compensation coils and the vertical compensation coil is modulated with
the period of the vertical deflection current such that a magnetic field
is generated in a direction opposite to the bias magnetic field thereby
changing the impedance of the horizontal compensation coils so as to
compensate for the center pincushion distortion on the left and right
sides of the screen.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view of a front screen, provided for schematically
illustrating a center pincushion distortion and the principle of
compensating for such a distortion.
FIG. 2 is a side view of a center pincushion distortion compensating
reactor for use in an image distortion compensating apparatus according to
the present invention;
FIG. 3 is a circuit diagram of an image distortion compensating apparatus
according to the present invention;
FIG. 4 is a front view of the front screen, provided for schematically
illustrating various image points on the screen;
FIG. 5 is a graph illustrating an example of the dependence of the
inductance of a first horizontal compensation coil L1 on the magnetic flux
density; and
FIG. 6 is a graph illustrating an example of the dependence of the
inductance of a second horizontal compensation coil L2 on the magnetic
flux density.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the present invention, a center pincushion distortion compensating
reactor is formed into a simplified construction including two horizontal
compensation coils, one vertical compensation coil, and a magnet for
applying a bias magnetic field to the horizontal and vertical compensation
coils. A horizontal deflection current is passed through the two
horizontal compensation coils being applied with the above-described bias
magnetic field. Furthermore, the vertical compensation coil is modulated
with the period of the vertical deflection current such that a magnetic
field is generated in a direction opposite to the bias magnetic field
thereby changing the impedance of the horizontal compensation coils so as
to compensate for the center pincushion distortion on the left and right
sides of the screen.
FIG. 2 is a side view illustrating an example of a construction of the
center pincushion distortion compensating reactor suitable for use in the
image distortion compensating apparatus according to the invention,
wherein only main parts are shown in the figure. In FIG. 2, the center
pincushion distortion compensating reactor 10 includes a case 11, cores
12-14, magnets 15 and 16, a first horizontal compensation coil L1, a
second horizontal compensation coil L2, and a vertical compensation coil
L3.
That is, the center pincushion distortion compensating reactor 10 includes
three compensation coils: the first horizontal compensation coil L1 wound
around the core 12, the second horizontal compensation coil L2 wound
around the core 14, and the vertical compensation coil L3 wound around the
core 13, as shown in FIG. 2.
A pair of magnets 15 and 16 is disposed such that one magnet is located at
one end of the set of three cores 12-14 and the other magnet is located at
the other end and such that one end has a south pole and the other end has
a north pole.
The two horizontal compensation coils L1 and L2 are wound in directions
such that the directions of magnetic fields generated by these coils L1
and L2 become opposite to each other.
The vertical compensation coil L3 is wound in a direction such that the
vertical compensation coil L3 generates a magnetic field in a direction
opposite to the direction of the magnetic field (bias magnetic field)
generated by the pair of magnets 15 and 16.
In the image distortion compensating apparatus according to the present
invention, the pincushion distortion on the left and right sides of the
screen is compensated for using the above-described center pincushion
compensating reactor 10.
The circuit configuration of the image distortion compensating apparatus is
described below.
FIG. 3 is a circuit diagram of the image distortion compensating apparatus
according to an embodiment of the invention. In FIG. 3, similar parts to
those in FIG. 2 are denoted by similar reference symbols or numerals. In
addition to those similar parts, the image distortion compensating
apparatus further includes horizontal deflection coils L4 and L5, vertical
deflection coils L6 and L7, resistors R1-R4, a variable resistor VR1, and
diodes D1 and D2.
In FIG. 3, the center pincushion distortion compensating reactor 10 is
shown in the form of an equivalent circuit whereas it has the physical
structure described above with reference to FIG. 2.
In FIG. 3, the horizontal deflection coils L4 and L5 and the vertical
deflection coils L6 and L7 are provided in the form of coils on a
deflection yoke. A sawtooth current with a horizontal period is supplied
to the horizontal deflection coils L4 and L5 from a horizontal deflection
circuit (not shown) and a sawtooth current with a vertical period is
supplied to the vertical deflection coils L6 and L7 from a vertical
deflection circuit, thereby deflecting the electron beam.
Although in the following description the deflection is assumed to be made
to the right, the image distortion compensating apparatus also operates in
a basically similar manner when the deflection is made to the left.
In the case of the deflection to the right, one of the horizontal
compensation coil, for example the first horizontal compensation coil L1,
generates a magnetic field in a direction opposite to the direction of the
magnetic field (bias magnetic field) generated by the two magnets 15 and
16. The other horizontal compensation coil, that is, the second horizontal
compensation coil L2, generates a magnetic field in the same direction as
the direction of the magnetic field (bias magnetic field) generated by the
two magnets 15 and 16.
In the following discussion, the operation is described for particular
points on the screen of the CRT.
FIG. 4 is a front view of the front screen, wherein the figure is provided
to schematically illustrate the center pincushion distortion and the
principle of compensating for such a distortion. In FIG. 4, A, B, E, and F
denote points lying on a horizontal line, and C, D, G, and H denote points
lying on an upper or lower horizontal line wherein the locations of points
C, D, G, and H correspond to the locations of points A, B, E, and F,
respectively.
In FIG. 4, the center pincushion distortion described above becomes great
in particular at points A and E on the screen. These points A and E are
located in a central part between the left and right ends B and F in the
horizontal direction, and thus these points A and E are called
central-area points.
In the case of the deflection to the right, if a center pincushion
distortion occurs, point A (a central-area point) shown in FIG. 4 is more
shifted toward the center of the screen than corresponding points C at an
upper or lower location, as shown in Fig. 1.
In the case of the deflection to the left, a center pincushion distortion
occurs in a fashion symmetric about the vertical line passing through the
center of the screen.
The change in the inductance of the coils depending on the location on the
screen is described below for particular points A-G defined in FIG. 4.
The first horizontal compensation coil L1 shown in FIG. 3 generates a
magnetic field in the direction opposite to the direction of the magnetic
field (bias magnetic field) generated by the two magnets 15 and 16.
When deflection is made to the right, the inductance of the first
horizontal compensation coil L1 varies depending on the magnetic flux
density and thus the inductance becomes such as shown in FIG. 5, at points
A, B, C, and D, respectively, shown in FIG. 4.
FIG. 5 illustrates an example of the dependence of the inductance of the
first horizontal compensation coil L1 on the magnetic flux density. In
this figure, the horizontal axis represents the location corresponding to
the magnetic flux density and the vertical axis represents the inductance.
On the other hand, the second horizontal compensation coil L2 generates a
magnetic field in the same direction as the direction of the magnetic
field generated by the two magnets 15 and 16.
When deflection is made to the right, the inductance of the second
horizontal compensation coil L2 also varies depending on the magnetic flux
density and thus the inductance becomes such as shown in FIG. 6 at
respective points A, B, C, and D shown in FIG. 4.
FIG. 6 illustrates an example of the dependence of the inductance of the
second horizontal compensation coil L2 on the magnetic flux density.
In FIGS. 5 and 6, an open arrow M represents the density of the bias
magnetic flux generated by the pair of magnets 15 and 16, a diagonally
shaded arrow A represents the density of the magnetic flux, at point A
(central-area point), generated by the horizontal compensation coils L1
and L2, a crosshatched arrow B represents the density of the magnetic
flux, at point B (at the right end), generated by the horizontal
compensation coils L1 and L2, and solid arrows C and D represent the
density of the magnetic flux, at points C and D at the top and bottom of
the screen, generated by the vertical compensation coil L3.
Furthermore, L(1A)-L(1D) denote the inductance of the first horizontal
compensation coil L1 at respective points A-D and L(2A)-L(2D) denote the
inductance of the second horizontal compensation coil L2 at respective
points A-D.
As shown in FIG. 3, the first horizontal compensation coil L1 and the
second horizontal compensation coil L2 are connected to each other in
series wherein the coils L1 and L2 are wound in opposite directions such
that they generate magnetic fields in directions opposite to each other. A
horizontal deflection current is applied from the horizontal deflection
circuit to the first horizontal compensation coil L1 and the second
horizontal compensation coil L2.
The sawtooth current applied to the vertical deflection coils L6 and L7 is
rectified by the diodes D1 and D2 and the rectified current is passed
through the vertical compensation coil L3. As a result, the vertical
compensation coil L3 generates a magnetic field, modulated with the period
of the vertical deflection current, in a direction opposite to the bias
magnetic field.
As a result, the inductance varies depending on the location (points A-D)
in FIG. 4.
Referring to FIG. 5, the change in the inductance of the first horizontal
coil L1 at the central-area point A and also at points C located above and
below point A is discussed below.
The first horizontal compensation coil L1 generates a magnetic field in the
direction opposite to the direction of the magnetic field generated, as
the bias magnetic field, by the pair of magnets 15 and 16.
Therefore, as shown in FIG. 5, the inductance L(1A) at point A in the
central area of the screen is determined by the magnetic flux density
given by the difference between the open arrow M (density of the bias
magnetic flux generated by the pair of magnets 15 and 16) and the
diagonally shaded arrow A (density of the magnetic flux generated, at
point A, by the horizontal compensation coil L1). That is, the inductance
L(1A) corresponds to the head of the shaded arrow A in FIG. 5. This
inductance L(1A) is approximately equal to the maximum inductance as shown
in FIG. 5.
The inductance L(1C) at points C on the screen corresponds to the head of
the solid arrow C, that is, the point obtained by shifting the point
indicated by the diagonally shaded arrow A to the left by an amount equal
to the length of the solid arrow C (density of the magnetic flux
generated, at the top and bottom points C on the screen, by the vertical
compensation coil L3). The inductance L(1C) (represented by the vertical
axis) at points C is nearly equal to the inductance L(1A) at point A.
That is,
L(1A).apprxeq.L(1C)
Referring now to FIG. 6, the change in the inductance of the second
horizontal coil L2 at the central-area point A and also at points C
located above and below point A is discussed below.
The second horizontal compensation coil L2 generates a magnetic field in
the same direction as the direction of the magnetic field generated by the
pair of magnets 15 and 16.
Therefore, in the case of the second horizontal compensation coil L2, the
inductance L(2A) at point A is determined by the magnetic flux density
given by the sum of the open arrow M (density of the bias magnetic flux
generated by the pair of magnets 15 and 16) and the diagonally shaded
arrow A (density of the magnetic flux generated, at point A, by the
horizontal compensation coil L2), as shown n FIG. 6. That is, the
inductance L(2A) corresponds to the head of the shaded arrow A in FIG. 6.
On the other hand, the inductance L(2C) at points C on the screen
corresponds to the head of the solid arrow C, that is, the point obtained
by shifting the point indicated by the diagonally shaded arrow A to the
left by an amount equal to the length of the solid arrow C (density of the
magnetic flux generated, at the top and bottom points C on the screen, by
the vertical compensation coil L3).
As a result, the inductance L(2C) at points C becomes greater than the
inductance L(2A) at point A. That is, L(2A)<L(2C)
The resultant total inductance L(1A)+L(2A) of the first and second
horizontal compensation coils L1 and L2 for point A relative to the
resultant total inductance L(1C)+L(C) for point C becomes such that
L(1A)+L(2A)<L(1C) +L(2C).
This means that the resultant total impedance at points C is greater than
that at point A, and thus the image size becomes smaller.
The change in the inductance at point B at the right end of the screen
shown in FIG. 4 and also at points D located above and below point B is
discussed below.
The first horizontal compensation coil L1 has an inductance L(1B) at point
B corresponding to the head of the crosshatched arrow B in FIG. 5, and
thus the inductance L(1B) at point B is equal to the inductance L(1C) at
points C.
On the other hand, the inductance L(1D) at points D corresponds to the
point obtained by shifting the head of the crosshatched arrow B to the
left by an amount equal to the length of the solid arrow D. That is, the
inductance L(1D) corresponds to the head of the solid arrow D.
Therefore, as can be seen from FIG. 5, the inductance L(1B) at point B
relative to the inductance L(1D) at points D becomes such that L(1B)
>L(1D).
In the case of the second horizontal compensation coil L2, the inductance
L(2B) at point B corresponds to the point obtained by adding the
crosshatched arrow B to the open arrow M (density of the bias magnetic
flux generated by the pair of magnets 15 and 16). That is, the inductance
L(2B) at point B corresponds to the head of the crosshatched arrow B.
On the other hand, the inductance L(2D) at points D corresponds to the
point obtained by shifting the head of the crosshatched arrow B to the
left by an amount equal to the length of the solid arrow D. That is, the
inductance L(2D) at points D corresponds to the head of the solid arrow D.
Thus, the inductance L(2B) at point B relative to the inductance L(2D) at
points D becomes such that L(2B)<L(2D).
If the inductances of the first and second horizontal compensation coils L1
and L2 are varied such that the resultant total inductance L(1B)+L(2B), at
point B, of the first and second horizontal coils L1 and L2 relative to
the resultant total inductance L(1D)+L(2D) at points D becomes such that
L(1B)+L(2B)=L(1D)+L(2D), then the inductance at point D becomes equal to
that at points D.
As a result, the image size becomes equal for point B and points D.
Thus, when the deflection is made upward or downward, the image size
becomes smaller in the central area of the screen whereas the image size
becomes constant at right and left ends of the screen. As a result, only
the center pincushion distortion is compensated for and thus a
high-quality image can be displayed on the screen.
The center pincushion compensating reactor used in the image distortion
compensating apparatus according to the present invention includes two
horizontal compensation coils connected to each other in series, one
vertical compensation coil, and a pair of magnets for applying a bias
magnetic field to the horizontal and vertical compensation coils.
Thus, the center pincushion compensating reactor includes a reduced number
of compensation coils compared to the conventional center pincushion
compensating reactor. This allows a reduction in cost. Furthermore, it
becomes possible to realize a small-sized image distortion compensating
apparatus with a simple structure which allows a high-quality image to be
displayed.
Furthermore, because a current obtained by rectifying the vertical
deflection current is used, the magnetic field includes a less amount of
undesirable change and the coil exhibits less core singing noise.
Furthermore, because a smaller intensity of bias magnetic field is
generated by the pair of magnets than generated by conventional magnets
arranged such that the same types of poles face each other, the influence
of the leakage magnetic field is minimized and thus the pair of magnets
may be disposed without having to take the landing into account.
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